﻿<p><em>IfcMaterialUsageDefinition</em> is a general supertype for all
material related information items in IFC that have occurrence
specific assignment parameters to assign a set of materials with
shape parameters to a reference geometry item of that
component.</p>
<p>There are two ways of assigning a set of materials with shape
parameters:</p>
<ul>
<li>a layer set to a reference curve - assigning a material layer
set with material layers having a sequence and thickness
parameter to a reference curve of an element - represented by the
'Axis' shape representation of that element</li>
<li>a profile set to a cardinal point - assigning a material
profile set with assigned profile geometry and insertion points
to a reference curve by an offset, called "cardinal point" - the
reference curve is represented by the 'Axis' shape representation
of that element</li>
</ul>
<p>Each instantiable subtype of <em>IfcMaterialUsageDefinition</em>
has to be assigned to a subtype of <em>IfcElement</em> by using the
objectified relationship <em>IfcRelAssociatesMaterial</em>; it is
only valid in conjunction with an element occurrence.</p>

<blockquote class="history">
HISTORY  New entity in IFC4
</blockquote>

<p class="spec-head">Informal Propositions:</p>
<ol>
<li>It is illegal to assign a subtype of
<em>IfcMaterialUsageDefinition</em> to a subtype of
<em>IfcElementType</em>, it shall only be assigned to an element
occurrence.</li>
</ol>